Poor flatness of the top surface of the base course

　　The flatness of the top surface of the base course is not good, which will directly affect the flatness of the asphalt surface course.

　　Because the asphalt surface is often very thin, if the flatness of the base course is poor, it is quite difficult to use the asphalt surface to make up. Due to the poor flatness of the base course, the thickness of asphalt on it is uneven. After the traffic is opened for a period of time, the density variation of asphalt surface mixture increases. Under the repeated driving load, the asphalt mixture is further compacted to increase the unevenness.

　　Uneven settlement of Subgrade

　　Due to the lax control of subgrade filling, improper foundation treatment or insufficient compactness of filled subgrade, the uneven settlement of subgrade will lead to the serious decline of pavement flatness. The roadbed is the foundation of the pavement. The uneven settlement of the roadbed will inevitably lead to the unevenness of the pavement, and the vehicle driving on the uneven pavement will produce a greater impact force, further increasing the unevenness.

　　The mix design is not ideal

　　The mix proportion design of asphalt pavement mixture has a direct impact on the indicators of the pavement. Good base mix and reasonable asphalt consumption will ensure the service life of the pavement. Otherwise, due to the unreasonable mix design, the asphalt mixture has poor high-temperature stability and water stability, resulting in serious ruts and cracks, which will seriously affect the pavement smoothness. In addition, the design of the base mix proportion will affect the overall strength of the semi-rigid base. As the direct bearing layer of the surface course, the strength of the base course will directly affect the indicators of the asphalt surface course.

　　Low level of construction technology and backward mechanical equipment

　　The unevenness of asphalt surface caused by the low level of construction technology often occurs. In the process of construction, the temperature control and joint treatment of the mixture can have a great impact on the flatness of the pavement; in addition, the unreasonable use of mechanical equipment has a great impact on the smoothness of the pavement, such as the instability of the structural parameters of the paver, the skidding of the walking equipment, the paving of the paver Unevenness of speed, violent mechanical starting and emergency braking as well as speed of feeding system will cause unevenness and wave of surface layer. Therefore, it is necessary to repeatedly improve the construction level and gradually improve the construction quality.